Do you have the domain set to Renew Later? = Yes in the Domains -> Registrations section of the panel?
If not, you should have received an email warning you that the domain was about to expire, so that you could manually renew the registration.
A note about the 'free' domain; Every year, just before your plan anniversary, you will receive one 'domain credit', allowing you to register or renew a domain for $0.00, you can choose to use this credit to renew the domain you specified when you signed up, or you can let that domain lapse and register an entirely different domain with the credit.
If that domain has lapsed, then yes you will need to register it again, but you should have a domain credit available to pay for it. Note; The domain credit doesn't actually show up anywhere (that I am aware of), but you will know when you have one as the price for a registration/renewal will be shown as $0.00.
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